Refrigerator system with refrigerant expansion through capillary tubes of adjustable length

ABSTRACT

A refrigerant system with mechanical compression and refrigeration cycle wherein the refrigerant is expanded through a set of capillary tubes of which the length is adjustable in response to a temperature transducer located within the evaporator section of the system. The means for regulating the capillary tubes length comprises a threaded cylinder slidably received within a tube, the trough of the screw thread functioning as a capillary tube. The system further comprises a trap means for capturing any liquid refrigerant escaping through the capillary tubes when the compressor is not running and for circulating the captured liquid refrigerant when the compressor is re-started.

United States Patent 1 [l 11 3,884,663 Funaro 1 May 20, 1975 REFRIGERATOR SYSTEM WITH 2,807,940 10/1957 Urban 62/511 REFRIGERANT EXPANSION THROUGH 3,677,028 7/1972 Raymond 62/222 CAPILLARY TUBES OF ADJUSTABLE LENGTH [76] Inventor: Ettore Funaro, Pizza Cimone 2,

Rome, Italy [22] Filed: May 6, 1974 [21] Appl. No.: 467,443

[30] Foreign Application Priority Data May a, 1973 Italy 4938/73 [52] 11.8. CI 62/222; 62/511 [51] Int. Cl. F25!) 41/04 [58] Field of Search 62/196, 216, 222, 511

[56] References Cited UNITED STATES PATENTS 2,148,413 2/1939 Labberton 62/511 2,532,019 11/1950 Goldberg 62/511 Primary Examiner-Meyer Perlin Attorney, Agent, or FirmFinnegan, Henderson, F arabow and Garrett [57] ABSTRACT A refrigerant system with mechanical compression and refrigeration cycle wherein the refrigerant is expanded through a set of capillary tubes of which the length is adjustable in response to a temperature transducer located within the evaporator section of the system. The means for regulating the capillary tubes length comprises a threaded cylinder slidably received within a tube, the trough of the screw thread functioning as a capillary tube. The system further comprises a trap means for capturing any liquid refrigerant escaping through the capillary tubes when the compressor is not running and for circulating the captured liquid refrigerant when the compressor is re-started.

4 Claims, 9 Drawing Figures PATENTED 3,884,663

SHEET 2 BF 2 1 REFRIGERATOR SYSTEM WITH REFRIGERANT EXPANSION THROUGH CAPILLARY TUBES OF ADJUSTABLE LENGTH The present invention relates to a mechanical compression refrigeration system with vapor-compression cycle in which the refrigerant fluid at its liquid state is supplied from a separator-receiver tank to the evaporator through the following components:

a regulating unit of the refrigerant flow rate which functions to change the flow resistance of the refrigerant by mechanically changing the length of a set of capillary tubes in parallel to one the others in response to changes of the condenser temperature;

a solenoid controlled valve at the outlet of said regulating unit which is controlled simultaneously with the compressor motor, which valve is closed when the compressor is not running;

a second set of parallel capillary tubes which are fed through said valve; and

a siphon suitably connected to a collecting tank which functions to avoid any piston knocking at the compressor due to the presence of liquid refrigerant therein.

According to an aspect of the invention, said refrigerant regulating unit is controlled by an electromechanism which, at its turn, is piloted by a sensing element of the condenser temperature.

It is known that in addition to the prior art refrigerators provided with expansion valves, other types are available wherein the means for restricting the flow from the condenser to the evaporator comprises capillary tubes which offer considerable practical advantages with respect to expansion valves because movable mechanical members are avoided thereby which involve sealing and wear problems. In fact restricting tubes are readily manufactured at low cost and long reliable operation of the machine is ensured thereby.

However capillary tubes also as they are presently employed have drawbacks which limit their use in refrigeration plants.

The two major drawbacks, which will be discussed hereinafter in more detail, are as follows:

1. A low coefficient of performance even at the environmental temperature for which the refrigerator has been designed.

2. Because the cross-section of a capillary tube is constant, there is no self regulation of the flow.

Due to these drawbacks, the refrigeration systems with capillary tubes as a restriction means of the refrigerant flow with air cooled condenser have a practical power upper limit in the order of 1.5 HP. Any increase of the system power brings about a tremendous increase of such drawbacks.

The aim of this invention is to maintain all the practical advantages of the capillary tubes expansion while eliminating the drawbacks, that is to attain a coefficient of performance of the system very close to the nominal coefficient pertaining to the ideal cycle operating between the same evaporation and condensation temperature whatever may be the environment temperature by which the condensation temperature is conditioned.

Another object of the invention is to provide a device adapted for functioning as a set of controllable capillary tubes which device, from the standpoint of operation life, is extremely reliable due to the absence of wearable components.

A further object of the invention is to provide an electromechanical control means adapted for actuating said flow regulating device in accordance with the temperature of the condensing space.

The above and other aspects of this invention will bacome apparent from the following description and attached drawings which illustrate as a non limitative example a preferred embodiment wherein a pipe from the receiver-separator tank feeds with equal flows said regulating device from two opposed inlets.

In the drawings:

FIG. 1 shows a schematic diagram of refrigeration system with expansion valve;

FIG. 2 shows a diagram of a refrigeration system with capillary tube expansion;

FIG. 3 shows a diagram of a refrigeration system according to this invention;

FIG. 4 shows in detail the flow regulating device and the related actuating mechanism;

FIG. 5 shows a detailed view of the syphon associated I to the collecting tank;

FIG. 6 shows a diagram of the electric circuit for controlling the device of FIG. 4;

FIG. 7 is an end view of the refrigeration system of FIG. 3 as seen from the high pressure side;

FIG. 8 is a side view of the refrigeration system of FIG. 3;

FIG. 9 is an end view of the refrigeration system of FIG. 3 as seen from the high pressure side, the louver being removed therefrom.

With reference to FIGS. 1 and 2, the two diagrams of the prior art systems are briefly described for better clarity. The cycle of both systems is the vaporcompression cycle that is: a fluid at its gaseous state (in general ammonia, Freon or methylchloride) is taken in by a compressor, its volume is reduced by compression and its temperature is increased; from the compressor the fluid is fed to an air or water cooled condenser wherein it is cooled and liquefied at constant pressure. The refrigerant from the condenser is collected at its liquid state into a receiver tank and therefrom it is supplied to an expansion valve and from this to an evaporator wherein it suddenly expands and is reverted to its gaseous state by heat transferred to it from the space to be refrigerated. From the evaporator the gaseous refrigerant returns to the compressor and the cycle starts up again.

A refrigeration system provided with expansion valve (FIG. 1) specifically comprises a compressor 1, a suction line 2 to compressor, a discharge line 3 from the compressor, a condenser 4, a liquid receiver-separator tank 5, an outlet pipe 6 depending from the top of tank 5 the open end of which reaches nearly the bottom of the tank, an expansion valve 7 and an evaporator coil 8. The purpose of tank 5 into which the still warm refrigerant from condenser 4 is fed is for causing said refrigerant to slowly flow over the inner sides of the tank walls down to the bottom thereof whereby the refrigerant is further cooled down to a value the closest possible to the room temperature. In fact it is known that the lower the temperature of the refrigerant outcoming from tank 5 the higher is the efficiency of the plant.

Through pipe 6 the refrigerant arrives at the automatic expansion valve 7 through which it is urged to flow when within the refrigerating coil 8 there is a vacuum produced by compressor 1.

On the other hand, a refrigeration system with capillary tubes expansion (FIG. 2) comprises a compressor 9, a suction line 10, a discharge line 1 l, a condenser 12, a capillary tube 13, a refrigerator 14.

Through the capillary tube 13 the refrigerant along the tube section between A and A undergoes a pressure drop the same way as across the expansion valve. The capillary tube is a very simple mechanical component and therefore more reliable and long lasting than an expansion valve, however it has the following disadvantages:

l. The capillary tube is in practice a passage perma nently open between the high pressure and the low pressure sections of the system and therefore there is always a refrigerant flow from the high pressure section to the low pressure section even if the compressor is not be running. As a consequence some amount of liquid refrigerant will invade the refrigerator coil 14. When the compressor starts up again, piston knocking can occur at the compressor which can cause failure of the same. For this reason in such type of systems the charge of refrigerant is reduced to a minimum and the receiver separator tank is suppressed.

Due to the absence of said tank the refrigerant entering the capillary tube is at a higher temperature than with the tank and therefore the efficiency of such systems is very low and, besides, it will become the lower the greater the system power. Hence the requirement arises of limiting the system power to 1.5 HP.

2. According to the prior art, neither the cross section nor the length of a capillary tube can be changed during the system operation and therefore an optimum efficiency will be attained at the average design environmental temperature while the efficiency will decrease at temperatures other than the design temperature, no means being provided for improving it. This can be considered to be a minor drawback in case of low operating temperatures in the order of -25C while it becomes a major deficiency for those systems which operate at temperatures in the order of C.

Let us now consider the diagram of a refrigerator according to this invention as shown in FIG. 3. It comprises a refrigerant receiver tank 19 to which a condenser 18 is connected and which is provided with a pipe 20 which depends from the top of the tank and reaches with its open end almost the bottom thereof, a compressor 15, a suction line 16 to compressor, a discharge line 17 from compressor and a normally closed solenoid controlled valve 27 included between a regulating device which as will be explained hereinafter functions as a set of adjustable capillary tubes, and a set of fixed capillary tubes 28.

The capillary tubes 28 of which three are shown in FIG. 3 are connected at one end thereof to a vertical conduit 22. Conduit 22 at the lower section thereof between dotted lines 45 and 46 of FIG. is formed as a syphon A which communicates with evaporator 24. Syphon A is connected to a collector vessel 49 by two ways: either through a capillary tube 48 (FIG. 5) and through a solenoid controlled valve which closes when compressor 15 is running and a check valve 47 which opens towards vessel 45 (see arrow in FIGS. 3 and 5) but closes the other way.

For better clarity, in FIG. 3 the lines which lead from the receiver-separator tank 19 to the regulating device 30 and to capillary tubes 28 are indicated by a continuous thick line.

When the compressor is operating the solenoid controlled valve 27 is open while it is closed when the compressor is not running.

Let us consider now the regulating device 30 and the related electronic control which are illustrated by FIGS. 4 and 6.

The regulating device substantially comprises a solid cylinder 35 of which two opposed end portions are threaded while a central section is turned down to a diameter smaller than the threaded portions. Cylinder 35 is slidably mounted within a coaxial tube 36 with precision fitting between the screw thread ridge and the inner surface of the tube. Tube 36 at one end thereof the left end in FIG. 4 has a chamber B which communicates with one of the two branches of pipe 20 which terminates at near the bottom of receiver 19. The other end of tube 36 penetrates one wall of a fluid tight housing 42 wherein the electromechanical device is contained for controlling the movement of cylinder 35 along tube 36.

Such electromechanical device comprises a motor 41 whose shaft 43 is threadingly fitted through a transverse arm 44 which therefore is moved along the motor shaft 43 when this is turned. Arm 44 is firmly attached to an extension of cylinder 35 and to a slider of a potentiometer so that when arm 44 moves along shaft 43 cylinder 3S and the potentiometer slider are also moved.

The center section of tube 36 is provided with two peripheral rows of through holes 37 which when cylinder 35 is moved leftward to end of stroke are both exposed, while when cylinder 35 is moved rightwards the left row is covered by the left threaded section of cylinder 35. Said center section of tube 36 including holes 37 is surrounded by a sleeve 38 which is provided with an outlet pipe 34.

According to a main feature of the invention, the screw threads with which the end sections of cylinder 35 are provided function as a pair of capillary tubes in parallel. In fact the refrigerant flowing through pipe 20 is divided in two streams one of which is inlet into chamber B and the other into housing 42. From both ends of cylinder 35 the refrigerant flows along the grooves of the threaded surface of cylinder 35, any direct flow from the cylinder ends towards the center section of tube 36 being prevented by the precision fitting between the screw thread ridge and the inner surface of tube 36. To this purpose the clearance between said two elements should be kept as low as 0.05 mm. By moving cylinder 35 Ieftwards from the end of stroke as shown in FIG. 4, the length of path of the refrigerant along either threading of cylinder 35 decreases. In this way a means is provided for regulating the flow rate of the refrigerant through a capillary tube.

The operation of electric motor 41 is controlled by an element sensitive to temperature which is located at a position where the temperature can be detected of the condensing refrigerant which in the case of an air cooled condenser is the room temperature.

The temperature sensing element is made to function as one of the two resistances of one of the two branches of a Wheatstone bridge (see FIG. 6). In FIG. 6, 50 and 51 are the leads of the electrical source of the bridge; 52, 39, S4 and 55 are the resistances of the same bridge; of said resistances: 39 is the changing resistance of potentiometer 39 included in said electromechanical device; 52, as already mentioned, is the resistance of the temperature sensing element and specifically its resistance coefficient is negative that is its resistance decreases when the temperature increases; 54 and 55 are fixed resistances.

In the same figure 56 indicates a voltage amplifier, 57 and 58 are two triggers, 59 and 60 are two relays adapted for inverting the rotational motion of motor 4], 62 is a source of electricity.

The operation of the regulating device is as follows:

When a change occurs of the condenser temperature, the electrical resistance of sensitive element 52 will also change whereby the Wheatstone bridge balance will be modified and a signal will be produced. Such signal, amplified by amplifier 56 is fed to triggers 57 and 58 by which relays 59,60 are controlled.

Relays 59, 60 will cause motor 41 to be connected to one or the other of the two polarities of source 62 in accordance with the direction of the bridge unbalance and motor 41 will be rotated accordingly. Because potentiometer 39 is driven by motor 41, resistance 52 will be changed until it becomes equal to the resistance of element 52 whereby the output from the Wheatstone bridge will be null and motor 41 will be stopped.

According to this invention, the above regulating device does not cover the whole range of length of the capillary path to be traversed by the refrigerant. In fact in no case a path of zero length will be required. For this reason, a set of capillary tubes of fixed length is provided which tubes are mounted in parallel with one the others and in series with the regulating device. The latter is designed for adding the required length of capillary path to the fixed length provided by the set of fixed capillary tubes 28.

According to an aspect of the invention a refrigerator system is provided in which although the refrigerant is expanded through capillary tubes a receiver tank 19 is included between the compressor and the capillary tubes of which tank the advantages have been already explained.

If no corrective measures were taken the presence of a large amount of liquid refrigerant within receiver tank 19 and within housing 42 of the regulating device could cause when compressor is stopped a flow of liquid refrigerant towards the evaporator 24 and from this to compressor 15 wherein it could cause damage when the compressor is started up again.

Two means are provided according to this invention for preventing such danger. A solenoid controlled valve 27 is inserted between the regulating device and the set of capillary tubes 28 which valve is closed when the compressor is not running.

Another safety means for preventing any flow of liquid refrigerant towards compressor 15 comprises a collecting tank 49 which is connected to a vertical manifold 22 which communicates with the set of fixed capillary tubes 28. Manifold 22 at its lower section is formed as a siphon (shown in FIG. 5 between dotted lines 45-46) that is the lower section of manifold 22 communicates with a downwardly arcuated pipe section which is followed by an uprising pipe section and by an upwardly arcuated pipe section and by a depending pipe section which is connected to evaporator 24. The lowermost point of the downwardly arcuated pipe section is connected to tank 49 through a normally open valve 29 that is a valve which is open when compressor 15 is not running and a check valve 47. A capillary tube 48 connects a position close to the bottom of tank 49 to a point along said uprising pipe section of said siphon.

The operation of said safety device is as follows:

Let us suppose that compressor 15 is not running and some leaking of liquid refrigerant occurs through valve 27. Then there will be a flow of liquid refrigerant to tank 49 through capillary tubes 28, a portion of the downwardly arcuated siphon, valve 29 and valve 47.

Simultaneously with the starting of compressor 15 valve 27 will open and valve 29 will shut. Due to the suction by compressor 15 the pressure within evaporator 24 will be lowered with respect to tank 49.

Due to check valve 47 no liquid refrigerant will flow through this valve and valve 29 towards evaporator 24; however some liquid refrigerant will flow through capillary tube 48 from tank 49. Such flow of liquid in addition to the liquid flowing through capillary tubes 28 will totally evaporate within evaporator 24 and will not cause any damage to the compressor.

What 1 claim is:

l. A refrigerator system with mechanical compression and refrigeration cycle comprising a compressor, a condenser connected to a discharge line, an evaporator connected to the suction line to compressor and a set of capillary expansion tubes in parallel to one the other between said condenser and said evaporator, which system further comprises a receiver tank connected to the outlet of condenser which receiver is provided with an outlet pipe of which the open end terminates at nearly the bottom of the receiver and which passes through the top thereof to communicate with a regulating device comprising at least a capillary tube of which the length is adjusted to fit the temperature changes of said evaporator the outlet of said regulating device being connected to one end of said set of capillary tubes of which the other end communicates with a vertical manifold; a siphon being provided at the lower end of said manifold; a collector tank being connected to said siphon at the lowermost point thereof through a check valve and through a capillary tube of which one end terminates at nearly the bottom of said tank and at the other end communicates with said siphon at a point higher than said lowermost point and located between the latter and the condenser; said system being further provided with a first solenoid controlled valve located between said regulating device and said set of fixed capillary tubes which valves is open when the compressor is running and with a second solenoid controlled valve located between said check valve and said siphon which valve is open when the compressor is not running.

2. A refrigerator system according to claim 1, wherein said regulating device comprises a solid cylinder of which two opposed end portions separate by a central portion of smaller diameter are threaded; which cylinder is slidably received with precision fitting into a tube of substantially the same length, said tube being provided with two peripheral rows of through holes which communicate with the space between the central section of smaller diameter of said cylinder when the latter is longitudinally centered with respect to said tube, the center section of said tube being enclosed within a cylindrical sleeve which extends at both ends beyond said rows of holes and which defines a fluid tight space around said tube which space communicates with said set of capillary tubes; said tube being closed at one end by a chamber defining cap the other end of said cylinder being open to the inner space of a housing wherein an electromechanism is contained for moving said cylinder in response to changes of the condenser temperature, said chamber and said inner space being both connected to said outlet pipe from the receiver tank.

3. A refrigerator system according to claim 2 wherein said electromechanism for moving said cylinder comprises a motor of which the shaft has a threaded extension which engages a threaded bore through a transverse arm of which one end is firmly attached to an extension of said cylinder and the other end is firmly attached to the slider of a potentiometer, the resistance of the latter being included in a Wheatstone bridge as one of the two resistances of a branch thereof while the corresponding resistance of the other branch of the bridge comprises a sensing element of the condenser temperature and the remaining resistances of the bridge are resistances of fixed value, the output of the bridge being connected to a pair of relays adapted for starting the compressor motor in either direction in accordance with the direction of the output current from the bridge.

4. A refrigerator system according to claim 3 wherein said temperature sensing element has a negative coefficient of resistance that is its resistance decreases when the temperature increases.

I i i 

1. A refrigerator system with mechanical compression and refrigeration cycle comprising a compressor, a condenser connected to a discharge line, an evaporator connected to the suction line to compressor and a set of capillary expansion tubes in parallel to one the other between said condenser and said evaporator, which system further comprises a receiver tank connected to the outlet of condenser which receiver is provided with an outlet pipe of which the open end terminates at nearly the bottom of the receiver and which passes through the top thereof to communicate with a regulating device comprising at least a capillary tube of which the length is adjusted to fit the temperature changes of said evaporator the outlet of said regulating device being connected to one end of said set of capillary tubes of which the other end communicates with a vertical manifold; a siphon being provided At the lower end of said manifold; a collector tank being connected to said siphon at the lowermost point thereof through a check valve and through a capillary tube of which one end terminates at nearly the bottom of said tank and at the other end communicates with said siphon at a point higher than said lowermost point and located between the latter and the condenser; said system being further provided with a first solenoid controlled valve located between said regulating device and said set of fixed capillary tubes which valves is open when the compressor is running and with a second solenoid controlled valve located between said check valve and said siphon which valve is open when the compressor is not running.
 2. A refrigerator system according to claim 1, wherein said regulating device comprises a solid cylinder of which two opposed end portions separate by a central portion of smaller diameter are threaded; which cylinder is slidably received with precision fitting into a tube of substantially the same length, said tube being provided with two peripheral rows of through holes which communicate with the space between the central section of smaller diameter of said cylinder when the latter is longitudinally centered with respect to said tube, the center section of said tube being enclosed within a cylindrical sleeve which extends at both ends beyond said rows of holes and which defines a fluid tight space around said tube which space communicates with said set of capillary tubes; said tube being closed at one end by a chamber defining cap the other end of said cylinder being open to the inner space of a housing wherein an electromechanism is contained for moving said cylinder in response to changes of the condenser temperature, said chamber and said inner space being both connected to said outlet pipe from the receiver tank.
 3. A refrigerator system according to claim 2 wherein said electromechanism for moving said cylinder comprises a motor of which the shaft has a threaded extension which engages a threaded bore through a transverse arm of which one end is firmly attached to an extension of said cylinder and the other end is firmly attached to the slider of a potentiometer, the resistance of the latter being included in a Wheatstone bridge as one of the two resistances of a branch thereof while the corresponding resistance of the other branch of the bridge comprises a sensing element of the condenser temperature and the remaining resistances of the bridge are resistances of fixed value, the output of the bridge being connected to a pair of relays adapted for starting the compressor motor in either direction in accordance with the direction of the output current from the bridge.
 4. A refrigerator system according to claim 3 wherein said temperature sensing element has a negative coefficient of resistance that is its resistance decreases when the temperature increases. 